Stretch-resistant papermakers belts having non-porous synthetic cables

ABSTRACT

This invention relates to conveyor belt-like papermakers&#39; fabrics for use in papermaking machines which comprise non-porous cables comprised of a plurality of yarns. Each yarn comprises at least two twisted monofilaments which are substantially circular in cross-sectional configuration.

BACKGROUND OF THE INVENTION

In the past, certain papermakers' belts or fabrics have been describedas being manufactured from porous cables comprising a plurality ofmonofilaments which are non-circular in cross-sectional configuration.Inthis connection, reference is made to Butler, U.S. Pat. No. 3,158,984.However, it is believed that such cabled structures would have severaldisadvantages which the present invention attempts to solve. Forexample, it is believed that such prior art structures would tend tostretch due to the void space encountered in the interstices of thecables making up the machine or longitudinal direction yarns of thefabric which interstices result from using such non-circularmonofilaments. By machine or longitudinal direction yarns it is meantthose yarns which extend in the direction of travel of such conveyorbelt-like fabrics. In addition, it is believed that such structureswould be subject to fill-up with pulp particles or fines or fillers inthe interstices of the porous cables, thus causing the papermakers' beltto drain in a non-uniform manner. Further, due to the likelihood of pulpfines and fibers entangling and building up in the interstices presentin the porous cables of such structures, it is believed that such beltswould exhibit poor sheet release. By sheet release, it is meant thesituation wherein the paper sheet is transferred from one section of apapermaking machine to another.

In the field of papermaker's fabrics it has also been known to make anduse fabrics woven from traditional multifilament yarns whichcharacteristically comprise a plurality of groups of twisted fibers orfilaments. However, it is believed that in some papermaking applicationssuch prior art fabrics have less dimensional stability in thecross-machine direction, and less desirable surface properties withregard to paper web formation, relative to the fabrics of the presentinvention. It is presently believed that these problems result from thestructure of such prior art fabrics utilizing multifilament yarns madefrom fibers or filaments each of which has a cross-sectional diameter of1.7 mils or less. While not wishing to be bound by any specific theory,it is thought that the constituents of the fibrous material in amultifilament yarn has a tendency to slide over one another, as forexample, when tension is applied to the fabric. This sliding then causesthe fabric to distort from the required shape causing sleasiness as wellas other undesirable characteristics.

It is believed that it is possible to overcome the forementionedproblems by utilizing a papermakers' belt which comprises yarns formedfrom circular monofilaments by which is meant monofilaments which arecircular in cross-sectional configuration. Such yarns are plied orcabled such that essentially non-porous cables are formed. Withoutwishing to be bound by any particular theory, it is thought that bymaking a papermakers' belt having such non-porous cables it is possibleto have a cabled structure with substantially no void space in thecables; hence reducing stretch when the belt is put on the drive rollsof a papermaking machine. It is also believed that by constructing apapermakers' belt utilizing monofilaments it is possible to overcome thesleasiness associated with prior are multifilament papermakers' belts.In addition, it is believed that the lack of avoids within the cabledstructure of the belt of the present invention will prevent plug-up bypulp fines and fillers which might cause an irregular drainage surfaceor problems with regard to sheet release.

In addition to overcoming the forementioned problems, it is believedthat papermakers' belts made in accordance with the teachings of thepresent invention provide a number of other advantages. For example,since such cabled yarns have a relatively high modulus of elasticity inaddition to being non-porous, when they are used in the load bearingdirection of a papermaker's belt it is possible to produce a belt havingsubstantial stretch resistance. It is believed that this allows for theproduction of belts having low drag characteristics and therefore betterwear characteristics, as well as an increase in the overall efficiencyof the papermaking operation. The term drag as used herein is meant torefer to the frictional interaction between the papermakers' belt andthe surfaces of the papermachine components. Further, by weaving withsuch cabled structures as in the present invention, it is possible, ifdesired, to increase the number of cross-machine direction strands orcables per inch without reducing the number of machine direction cablesper inch unless such a reduction is desired. By so increasing the numberof cross-machine direction strands or cables per inch it is possible, ifdesirable, to produce a fabric having square interstices without havingto reduce the number of machine direction cables per inch to effect sucha result. Unexpectedly, it has been found that such fabrics haveexcellent pulp fine retention properties as well as superior crossmachine direction stability and shove resistance. By shove resistance itis meant the ability of adjacent yarns or cables to maintain theirposition relative to one another when lateral forces act on their sidewalls. It is thought that the improved fine retention properties resultsfrom the use of a fabric having square interstices.

Without wishing to be bound by any particular theory, it is believedthat a greater number of cross machine direction strands or cables canbe included in fabrics as described above because prior to finishing themachine direction cables of the present invention have a relatively highdegree of deformability, thus allowing more cross machine directionstrands or cables to be inserted for a given unit of belt width. Hence,using such cables not only allows for the introduction of a greaternumber of cross machine direction strands or cables in the fabric butalso enables the manufacturing of such fabrics at lower loom loads thanwould otherwise be possible without the use of such cables. It isthought that lower loom loads can be utilized because such cables areeasily deformable before finishing and hence give less resistance toforces exerted during weaving.

Thus, it is an object of the present invention to provide a papermaker'sbelt in which non-porous cables extend in the machine direction and arecomprised of yarns formed from monofilaments which are circular incross-sectional configuration.

It is a further object of this invention to provide a papermakers' belthaving improved stretch resistance in comparison to prior artpapermaker's fabrics.

Another object of the present invention is to provide a papermakers'belt which provides for improved retention of pulp fines.

A still other object of this invention is to provide a means ofincreasing the number of cross machine direction strands or cables perinch in a papermakers' fabric without reducing the number of machinedirection cables per inch while utilizing low loom loads.

A further object of the present invention is to provide a papermakers'belt having improved dimensional stability and shove resistance.

A still further object of the present invention is to provide apapermakers' belt having improved drainage uniformity.

Another object of the present invention is to provide a papermakers'belt having improved sheet release properties.

Yet, another object of the present invention is to provide apapermakers' belt having reduced pulp fine and filler build-up in thecables comprising the belt.

SUMMARY OF THE INVENTION

These and other objects as will be apparent to those individuals who areskilled in the art can be achieved from the practice of the presentinvention in one embodiment of which a papermakers fabric comprisesnon-porous synthetic cables which extend in the longitudinal directionof such fabric. Each of the cables comprise at least three yarns andeach of such yarns comprise two or more monofilaments which are circularin cross section and have a diameter of at least 3 mils.

An understanding of this invention may be had from the detaileddiscussion which will follow and from an examination of the drawingsincluded herein which:

FIG. 1 is a perspective view of a papermakers' belt embodying thepresent invention.

FIG. 2 is a fragmentary plan view of a portion of the papermakers' beltshown in FIG. 1.

FIG. 3 is a sectional view along line 3--3 in FIG. 2.

FIG. 4 is an enlarged fragmentary view showing one form of a cable ofthe present invention.

FIG. 5 is a cross-sectional view taken along lines 5--5 of FIG. 4.

FIG. 5A is a cross-sectional view of a cable of the present inventioncomprising ultra high modulus strands.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to FIGS. 2 through 5, which are views of a portion of thepapermakers' belt 2 shown in FIG. 1, non-porous cables 8 extend in themachine direction and comprise yarns 2, 4, 6 which have been plied orcabled together. Yarns 2, 4, 6 each comprise substantially circularmonofilaments which have been twisted together. By the forementioned useof the term cable it is meant a structure which is made up of pliedyarns. A plied yarn is taken for present purposes to mean a yarn formedby twisting together two or more monofilaments. Generally, the termmonofilament as used herein is meant to refer to a single filament madefrom man-made fibers such as polyamide, acetate, rayon, polyester,orlon, fiberglass and the like, which is circular in cross section andhas a diameter of at least three mils. The forementioned cables of thepresent invention extend in the machine direction and may also be usedin the cross machine or transverse direction as well if desired althoughany type of yarn or strand suitable for use in papermakers fabrics maybe used in the transverse direction. For example, it has been found thatpolyester monofilaments are particularly useful in the transversedirection. It should be understood that the term papermakers' belt asused herein includes forming fabrics, dryer fabrics and felts, and thelike, and is meant to include such fabrics and felts as may be endlesswoven or woven flat and then joined so as to form a conveyor belt-likestructure. Any monofilaments may be used to form the yarns whichcomprise the cables of the present invention and the recitation ofmonofilaments made from a specific material is not meant to limit thescope or range of the present invention.

If it is desirable to further increase the stretch resistance ofpapermakers fabrics of the present invention, other strands orstrand-like material can be used in combination with the cablesdescribed herein. In addition to ordinary strands, stretch resistancecan be increased by including ultra high modulus strands in combinationwith the cables of the present invention. For example, if it is desiredto produce cables having a very high initial modulus and a consequentlow elongation, the cables of the present invention can be combined withsynthetic multifilament fibers such as -poly (para-phenyleneterephthalamide) and is sold under the trademarks Kevlar and Kevlar 29and manufactured by E. I. Du Pont De Nemours & Company. In oneembodiment as depicted in FIG. 5A and described below, suchmultifilament fibers may be twisted with the monofilaments comprisingthe individual yarns which make up the cabled structure so long as eachyarn contains at least two monofilaments. However, any suitable mannermay be utilized in combining additional strands with the yarns whichmake up the cables of the present invention.

In the preferred embodiment depicted in FIGS. 2 through 5 of thedrawings, cables 8 are made up of a plurality of yarns 2, 4, 6 whichhave been plied together. Each cable 8 can be achieved as shown in thedrawings by plying a plurality of yarns 2, 4, 6 each one of whichcomprises two or more polyester monofilaments which are substantiallycircular in cross section and which have been twisted together. Forexample, yarn 2 preferably comprises synthetic monofilaments 2', such aspolyester monofilaments, which are circular in cross section and whichare twisted together. Similarly, yarns 4 and 6 comprise suchmonofilaments 4' and 6', respectively. The yarns 2, 4, 6 can be pliedaround each other after the constituent monofilaments of each yarn havebeen twisted together as shown in FIGS. 4 and 5. In a further embodimentthe yarns 2, 4, 6 could be plied around a central core yarn (not shown)so as to form the various cable constructions which can be utilized invarious embodiments of the present papermakers' belt. In a furtherembodiment, and as noted above, if it is desired that the cables 8 havean extremely high stretch resistance or other properties achievable byincorporating ultra high modulus strands, then the cables of the presentinvention could include ultra high modulus multifilaments such asKevlar. For example, as depicted in FIG. 5A one of the constituentmonofilaments 2', 4', 6' in one or more of the yarns 2, 4, 6 could bereplaced with multifilament Kevlar 2", 4", 6" or similar material, andthe remaining monofilaments would comprise polyester or polyamide orsome other suitable material. Alternatively, in the cable depicted inFIG. 5, plied yarn 6 can consist of one type of monofilaments 6' and beplied with yarns 2 and 4 of some other type of monofilaments. Usingthese methods, it is possible, if desirable, to adjust the modulus ofthe papermakers' belt so as to be suitable for a variety of end-useapplications by selectively varying the types of monofilaments and otherstrands used in each cable.

In twisting the monofilaments or other constituents which comprise theplied yarns, any of the common twist configurations such as S or Z canbe used and the recitations of these specific configurations are notmeant to exclude or preclude others. In plying the yarns which make upthe cable the only requirement is that it be plied or cabled in adirection opposite to that used in twisting the monofilaments which makeup the yarn. For example if the monofilaments have been subjected to anS twist it will be necessary for the yarn to be plied with a Z twist,the choice of twisting and plying or cabling being mainly dependent onthe intended end use of the present invention.

If desired, fabric stability can be increased by resin treating thecables usd in the production of the fabric. In addition, if desired anyadditional strands or strand-like materials used can also be resintreated.

By way of examples, and without intending to limit the scope of suitableresins which might be used in the present inventions, such resins asnylon resins, water-based acrylics in which two examples are RhoplexAC-201 (produced by ROHM & HASS) and Hycar 2600 × 172 (produced by B. F.Goodrich), phenolyic resins and amino resins such as American CyanamidsAerotex M-3 are suitable for use in practicing the present invention.

The above-mentioned resins have the following chemical and physicalidentification:

    ______________________________________                                        Rhoplex® AC 201 (Rohm and Haas Co.)                                       Thermosetting Acrylic Emulsion                                                Solids Content        46 ± 1%                                              pH                    9.0 to 10.0                                             Emulsifying System    Nonionic                                                Approximate Viscosity as packed, cps                                                                60                                                      (#2 spindle, 60 rpm at 25° C,                                          Brookfield LVF Viscometer)                                                    Minimum Film Forming  +29                                                     Temperature, ° C                                                       Aerotex® M-3                                                              (American Cyanamid Company)                                                   A melamine-formaldehyde condensate                                            (trimethylol melamine type)                                                   Active Ingredients    80%                                                     pH                    8.5 - 9.0                                               Solubility            Soluble in water in all                                                        proportions                                            lbs./gal.             10.0                                                    Hycar® 2600X 172 Acrylic Latex                                            Water dispersion of modified                                                  hard acrylic polymer                                                          Emulsifying System    Anionic                                                 Density Latex, lbs./gal.                                                                            8.7                                                     Solids Content        50%                                                     pH                    2.5                                                     Viscosity (Brookfield, #2, 60 rpm)                                                                  200 cps                                                 Surface Tension (dynes/cm)                                                                          50                                                      Glass Transition Temp. (° C)                                                                 +33                                                     Special Gravity                                                               Latex                 1.05                                                    Solids                1.10                                                    ______________________________________                                    

One desirable resin coating method might be to use a two step resintreatment, whereby first a thermo-setting acrylic resin is applied andthen a phenolic resin. Such a suitable method and apparatus for applyingthe resin is known to be described in Christie, et al. U.S. Pat. Nos.3,252,821 and 3,149,003.

It will, of course, be apparent to those skilled in the art that thepresent invention may be practiced in a wider variety of embodimentsthan have been set forth in detail at present without having tomaterially depart from the spirit and scope of the teachings containedherein. It also should be understood that in the foregoingspecification, specific embodiments and components of the presentinvention have been used for illustrative purposes and discussed by wayof example and not by way of limitation, and therefore this inventionmay be practiced by those skilled in the art by utilizing a wide varietyof materials and configurations without departing substantially from thetrue spirit of the present invention.

I claim:
 1. A stretch resistant papermakers' fabric for use on apapermaking machine comprising nonporous synthetic cables which extendin the longitudinal direction of said fabric and comprising syntheticyarns which extend in the transverse direction of said fabric and,wherein each of said cables comprise at least three yarns and each ofsaid yarns of said cables comprising two or more monofilaments which arecircular in cross section and have a diameter of at least 3 mils andwherein said yarns which comprise said cables comprise monofilaments ofpolyester and include ultra high modulus multifilaments.
 2. A fabric asrecited in claim 1 wherein said multifilaments comprise poly(para-phenylene terephthalamide).
 3. A fabric as recited in claim 1wherein said yarns of said cables include multifilament poly(para-phenylene terephthalamide), and said cables are resin coated.
 4. Afabric as recited in claim 3 wherein said cables are resin coated with athermo-setting acrylic resin.
 5. A fabric as recited in claim 1 whereinsaid transverse direction yarns comprise polyester monofilaments.